This is a recent problem for me. I haven't installed anything or had hardware changes. But one day I booted up my computer it had a black screen, until it finished the boot up process into Windows 7. Everyday since then each time I boot up the amount of time it takes for the screen to appear is longer and longer. Today it's about 21 minutes. Avg. an extra minute per day.. Two weeks ago it wasent bad, I'd just wait three extra minutes,... Eventually ten extra minutes ..but now I'm approaching a half hour of black screen before the black screen pops away.
This is what I've tried. Disconnecting all hardware and re connect. Ram cache flush, adjusting screen resolution and refresh rates, checked for new updates on all hardware and software. Disconnecting motherboard battery, trying new monitors and cables.
I suspect it's a motherboard issue, but I have no idea.